When I open ‘pavucontrol’ utility on server, navigate to Input Devices tab and set ‘Monitor of NoMachine Output’ as fallback source instead ‘NoMachine Microphone’, delay value decrease to ~0.5 second. It fixed my issue, buy I must do that manually after each connect to server.
My problem is much more serious. Ubuntu 16.04 is server system, Ubuntu 18.04 is client. Audio delay (I mean voice/microphone forwarding from client to server) more than 2 seconds on the server. On client voice is realtime.
Build 6.9.2_1_amd64 free version on both sides.
Gnome fallback mode on both sides.
No Phonon. Pulseaudio was fully reinstalled on the server. Various settings on Server was implemented (video/audio quality, videocodecs, etc. was changed). Delay does not changed.